Project Summary/Abstract c-Jun N-terminal protein kinase (JNK; also known as stress-activated protein kinase, SAPK) plays a central role in proliferation, differentiation, programmed cell death and transformation. Overwhelming evidence implicates that JNK is a key regulator in many pathophysiological events including inflammation, immune responses, diabetes, obesity, heart hypertrophy, and oncogenesis. However, the molecular mechanism by which JNK activity is regulated by distinct extracellular stimuli is still incompletely understood. In this proposal, we will investigate whether JNK activation by distinct extracellular stimuli is mediated by a JNK signalsome, which is a dynamic protein complex that includes JNK-associated, stimulus-specific modulators or regulators (SMOR). Using both genetic and biochemical approaches, we recently found that JNK forms a protein complex and its activity can be regulated by stimulus-specific regulators. Furthermore, we found that two ubiquitously expressed JNK isoforms, JNK1 and JNK2, are differentially regulated by various extracellular stimuli. Thus, we hypothesize that the stimulus-specific JNK signalsome determines JNK activation by environmental stimuli and/or embryonic development cues. This proposal is novel, as it will identify the JNK signalsome a dynamic and functional protein complex for JNK activation, and determine the molecular mechanisms by which JNK1 and JNK2 are differentially regulated at different developmental stages. This study will put forward a novel paradigm regarding the molecular mechanism underlying the regulation of the JNK mitogen-activated protein kinase subfamily by extracellular stimuli and the rationale in targeting JNK for prevention and treatment of human diseases and cancer. Project Narrative The cell signaling network is composed of many important signaling pathways, including the stress activated protein kinase JNK pathway, which plays a central role in many pathophysiological events and has been implicated in numerous human diseases and certain types of cancer. However, it is difficult to target JNK for therapeutic purposes without affecting normal physiological functions in human. This proposal studies the molecular mechanism by which stimulus-specific modulators or regulators control JNK activation by specific extracellular stimuli, thereby providing a novel strategy to target the unique modulators or regulators of JNK, rather than JNK itself, for prevention and treatment of human diseases and cancer.